Apios americana, sometimes called the potato bean, hopniss, Indian potato, hodoimo, America-hodoimo, American groundnut,or groundnut (but not to be confused with other plants sometimes known by the name groundnut) is a perennialvine that bears edible beans and large edible tubers.[1] Its vine can grow to 1–6 m long, with pinnate leaves 8–15 cm long with 5–7 leaflets.[1] The flowers are usually pink, purple, or red-brown, and are produced in dense racemes 7.5–13 cm in length.[1] The fruit is a legume (pod) 5–13 cm long.[1] Botanically speaking, the tubers are rhizomatous stems, not roots.[2] Its natural range is from Southern Canada (including Ontario, Quebec, and New Brunswick) down through Florida and West as far as the border of Colorado.[1]

The tubers are highly palatable with culinary characteristics of a potato, although the flavor can be somewhat nuttier than a potato and the texture can be finer.[3] Studies in rats suggest that raw tubers should not be consumed because they contain harmful protease inhibitors that are denatured by cooking.[4] Tubers contain roughly three times the protein content of a potato (16.5% by dry weight), and the amino acid balance is good with the exception of cysteine and methionine.[5]Apios americana tubers were found to have a protein concentration of 15–30 mg/g.[6] This was similar to that of other species in the Apios genus, Apios carnea and Apios fortunei.[6] However, A. americana had larger levels of genistein than the other two species.[6] The fatty acid content of tubers is approximately 4.2% to 4.6% with linoleic fatty acids predominating.[7] Thirty-six percent of the fresh weight of a tuber is carbohydrate (primarily starch).[8] The tubers are also an excellent source of calcium and iron.[8] Calcium content is 10-fold greater than a potato and iron is 2-fold greater than a potato, although vitamin C was considerably less than a potato.[8] The tuber and the flower are also full of mono and oligosaccharide.[9] The tuber has more monosaccharides and oligosaccharides than the soybean, potato, and sweet potato.[9] In addition, the tubers appear to have numerous health promoting factors. Hypertensive rats that were fed powdered tubers as 5% of their total diet experienced a 10% decrease in blood pressure and also a reduction in cholesterol and triglycerides.[10] It has been shown that the tubers contain genistein and other isoflavones that have various health benefits, including an anticarcinogenic function against colon, prostate, and breast cancer.[11][12] Genistein-7-O-gentiobioside is a novel isoflavone that is found in the American groundnut.[13] Extract from the American groundnut was shown to not have anti-oxidative activity itself, but to drive the anti-oxidative pathway in cells.[13] Human breast carcinoma MCF-7 cells were pretreated with the extract of A. americana for 24 hours.[13] Subsequent analysis showed an increase in expression of heme oxygenase-1, a protein induced during oxidative stress.[13] The American groundnut, like soybean, is a great source of isoflavone.[13] Furthermore, a study on A. americana and it’s flower shows that the flower of the particular plant is not toxic to mice.[14] In fact, the flower was shown to lower plasma glucose levels in diabetic mice.[14] The flower was shown to have an inhibitory activity on maltose and an anti-hyperglycemic effect in mice suggesting that not only is it a viable and novel food source for the general population, but also in the prevention of diabetes.

The only place in the world today where American groundnut are commercially farmed in any significant quantities is in Japan. Before American groundnut was introduced to Japan, the people on the main island of Honshu and the Northern island of Hokkaido were already familiar with a native, wild plant there called hodoimo (Apios fortunei) that was occasionally eaten as an emergency food.[8] It is believed that sometime during the Meiji period (1868-1912) American groundnut was accidentally or deliberately brought to Japan.[8][10][12][15][16] One theory is that American groundnut was accidentally brought to Japan as a stowaway weed among apple seedlings imported from North America.[10][12] Another theory is that American groundnut may have been deliberately brought to Japan in the middle of the Meiji period as an ornamental flower.[8][15] It is now considered a culinary specialty of the Aomori prefecture where American groundnut agriculture is centered and where it has been eaten for more than 100 years.[17][18] Although American groundnut agriculture is primarily identified with agriculture in the Aomori prefecture, it is grown in the nearby prefectures of Akita and Miyagi as well.[16] In addition, it is known to be grown in the Southern part of Honshu in the Tottori prefecture, and radioactive testing records following the Fukushima nuclear disaster record cesium testing of American groundnut agricultural products in the central prefecture of Tochigi.[16][19] An important part of the spread and popularization of American groundnut consumption in Japan has been the efforts of Dr. Kiyochika Hoshikawa to promote the cultivation of this crop in Japan and the flurry of scientific articles on the health benefits of eating American groundnut tubers.[10] Japanese websites that sell American groundnut continue to emphasize its health benefits in their marketing efforts.[18][20] There are reports of American groundnut cultivation in South Korea as well where it is grown for its nutritional benefits[21]

The tubers were a staple food among most Native American groups within the natural range of the plant.[22] In 1749, the travelling Swedish botanist Peter Kalm writes, “Hopniss or Hapniss was the Indian name of a wild plant, which they ate at that time... The roots resemble potatoes, and were boiled by the Indians who ate them instead of bread.”[22] Strachey in 1612 recorded observations of the Native Americans found in Virginia: “In June, July, and August they feed upon roots of tockohow, berries, groundnutts, fish, and greene wheate...”[22] In Eastern Canada, the Jesuit missionary, Le Jeune, observed that the Native Americans there would, “eat, besides, roots, such as the bulbs of the red lily; ... another that our French people call ‘Rosary’ because it is distinguished by tubers in the form of beads.”[22] The early author Rafinesque observed that the Creeks were cultivating the plant for both its tubers and seeds.[22] The author Brinton wrote in 1885 in regards to the Lenape people, “Of wild fruits and plants they consumed the esculent and nutritious tubers on the roots of the Wild Bean, Apios tuberosa... which the Indians called hobbenis...”[22] In 1910, Parker writes that the Iroquois were consuming significant quantities of groundnuts up until about 30 years before his writing.[22] The Paris Documents of 1666 record that the sixth tribe of the second division of the Iroquois were identified as, “that of the Potatoe, which they call Schoneschironon” and an illustration of tubers is found in the Paris Documents with the explanation, “This is the manner they paint the tribe of the Potatoe.”[22] The author Gilmore records the use of groundnuts by the Caddoan and Siouan tribes of the Missouri river region, and the authors Prescott and Palmer record its use among the Sioux.[22] The Native Americans would prepare the tubers in many different ways. Many tribes peeled them and dried them in the sun, such as the Menomini who built scaffolds of cedar bark covered with mats to dry their tubers for winter use.[22] The Menomini would sometimes dry the tubers in maple syrup or make a preserve of Groundnut tubers by boiling them in maple syrup.[22] The Potawatomi traditionally boiled their tubers.[22] The Meskwaki and Chippewa would peel, parboil, slice, and dry the tubers, and the Chippewa were fond of using the tubers as a sort of seasoning in all their foods.[22]

The Europeans learned to use the American groundnut from the Native Americans. As a result, the American groundnut became interwoven with the history of the American colonies and Europe. The early traveler John Brereton was sustained by the “good meat” and “medicinable” qualities of American groundnut during his travels in New England in 1602.[22] In 1613, the followers of Beincourt at Port Royal ate the tubers to help them live in the New World.[22] The American groundnut was an important factor in the survival of the Pilgrims during the first few winters of their settlement.[23] In 1623 the Pilgrims, “having but a small quantity of corn left,” were “enforced to live on groundnuts... and such other things that the country afforded... and were easily gotten...”.[22] The Pilgrims were taught to find and prepare American groundnut by the Wampanoag people.[3] It seems quite probable that groundnut would have been eaten at the harvest festival of November 1621 that is regarded as the first Thanksgiving, although only venison was specifically named as a food item at this meal by a Pilgrim eyewitness account. It is believed that American groundnut may have made it back to Europe as early as 1597, and it was listed as a European garden crop in 1885.[1] It was evaluated as a possible alternative potato crop in Ireland in 1845 during the potato famine.[1] These early introductions to Europe appear to have resulted in little or no assimilation of the new food into the European diet.[1] A primary reason for this lack of assimilation was that the two-year cycle for an acceptable tuber yield did not match the cropping systems that were familiar to Europeans.[1]

American groundnut is generally considered to be an undomesticated crop. Gretchen Beardsley in her 1939 description of the Native American utilization of American groundnut states that several historical sources describe the “cultivation” of American groundnut by Native Americans, although she dismisses the ambiguous term “cultivation” as perhaps the transplantation of tubers near a settlement, and she quotes the historical author Waugh on this subject of cultivation: “sometimes planted in suitable locations, though they are not, strictly speaking, cultivated.”[22] It appears that all subsequent authors on American groundnut have followed Gretchen Beardsley’s interpretation of “cultivation” when referring to the early utilization of American groundnut by Native Americans. In 1985, Dr. William J. Blackmon, Dr. Berthal D. Reynolds, and their colleagues at Louisiana State University in Baton Rouge LA began a program of deliberate domestication of American groundnut with the primary goal of developing an American groundnut that can produce a significant yield in a single season.[1][3][23] Early trials identified LA85-034 as a promising cultivar, with “elongate tubers of uniform, medium size with light brown skin and little extra rhizomatous material”.[23] By 1988, they had collected wild seeds and tubers from 210 plants found in 19 states, although the bulk of their selections came from the state of Louisiana.[1] From these wild materials, and a small number of single crosses, they rigorously selected for plants that met their primary breeding goals of (1) larger tuber size, (2) denser tuber set, (3) single season production, and (4) productivity in untrellised cultivation.[1] The American groundnut domestication program at Louisiana State University continued in various forms until the mid-1990s.[3] Cultivars from this program can still occasionally be found available from small seed companies. From 1985 to 1994, an Apios breeding program took place that resulted in the collection of over 200 wild accessions. These accessions underwent hybridization and selection and over 2200 lines were assessed.[24] Of these lines, only 53 genotypes were kept for further analysis. Three different locations and three different growing conditions—field, pots, and grow-bags—were utilized. There was significant variation found between almost all of the 20 genotypes in the field growing condition. Furthermore, inter-node length, plant vigor, and stem diameter during plant growth was positively correlated with the plant yield below ground.[24] There were four distinct genotypic clusters found in this collection of Apios lines. Several genotypes yielded large plants in all locations maxing up to 1.5 kg of below ground tuber.[24] This suggests that the plant has a good ability to adapt and grow in a wide variety of locations and conditions. Furthermore, the superior germplasm identified in this project may be suitable as cultivars, and will aid in further development of Apios lines as a crop.[24] The largest germplasm collection of Apios americana cultivars today is found at Iowa State University under the direction of Dr. Steven Cannon.[21] It is maintained there for scholarly and academic use. Research continues on the domestication of American groundnut at Iowa State University.[21][25] Despite these efforts at domestication, the American groundnut remains largely uncultivated and underutilized in North America and Europe.[3] There are challenges to breeding and domesticating this plant, as well.[26] There seems to be a partial self-incompatibility with Apios breeding and manual pollinations resulting in rare seed-sets.[26] Disadvantages in Apios as a crop are its vining habit.[27] The crop also has small tuber size for most genotypes.[27] These sizes are typically smaller than 50 grams, however some do average around 100 grams.[27] The tuber plant is also difficult to harvest because of the "beads on a string" arrangement on stolons that extend for over a meter .[27]

American groundnut fixes its own nitrogen, which could be a great advantage in comparison to other roots crops, such as potatoes, true yams, and sweet potatoes, that do not fix their own nitrogen and require large nitrogen fertilizer inputs.[28] American groundnut can be nodulated by bacterial strains that are normally found in symbiosis with soybeans or cowpeas.[28] Research has been done on the potential of the soybean strain B. japonicum to nodulate American groundnut.[28] It was found that plants nodulated with B. japonicum yielded ~30% better than unnodulated plants if no nitrogen fertilizer was used.[28] It was also determined that nodulated plants partitioned more carbon into non-edible shoots when they were given nitrogen fertilizer whereas unnodulated plants responded to nitrogen fertilizer with greater tuber yields than nodulated plants.[28] This data suggests that nitrogen fertilization may be required to maximize tuber size and yields in A. americana.[28]

American groundnut is normally 2n=2x=22, diploid, but both diploid and triploid forms exist.[1] Only diploids are capable of producing seeds; triploids will produce flowers but not seeds.[29] Thus, triploids are entirely dependent on tuber division for propagation whereas diploids can be propagated through both seeds and tubers.[29] Other than seed production, there are no easily identifiable differences between diploids and triploids.[29] Triploids are generally found in the Northern part of American groundnut’s range whereas diploids predominate in the Southern part of the range.[29] Triploids have been identified in the provinces or states of New Brunswick, Quebec, Ontario, Connecticut, Vermont, Massachusetts, New York, Pennsylvania, Ohio, New Hampshire, Rhode Island, Wisconsin, and Iowa.[29][30][31] A few diploids have been found in the Northeastern part of the range, such as along the Black River in Central Ontario.[30] All samples tested in the Southeastern United States have been found to be diploid.[29][30][31]